A. Field of the Invention
This invention relates to refractory structures and, in particular, to a perforated inner retaining wall made of refractory block usable in heat exchange apparatus.
B. Prior Art
Recently, with the advent of ever-higher energy cost figures, there has been a correspondingly increased demand for apparatus which can conserve heat thereby reducing fuel costs. One such apparatus which is usable especially in thermal regenerative apparatus for pollution control, for example, is shown in U.S. Pat. No. 3,895,918 issued to James H. Mueller on July 22, 1975. As shown in that patent, there is a central high temperature combustion or incineration chamber surrounded at equi-angularly spaced intervals by a number of contiguous heat-exchange sections. These sections communicate with the combustion chamber and with an external supply of pollutants such as noxious effluents from industrial processes. The effluents are applied by employing automatic dampers to predetermined ones of the heat-exchange sections during any given cycle of operation. In each section, there is a heat-exchange bed made of a number of ceramic heat-exchange elements which are retained outwardly by a perforated steel wall and inwardly (closest to the combustion chamber) by another perforated or louvered metallic wall. Since a great quantity of heat exchange elements are poured into the space between these two retaining walls, there is a great amount of lateral thrust exerted by their combined weight.
When the effluents are passed through a predetermined one or ones of the heat-exchange sections during a processing cycle, their temperature is increased by the residual heat in the ceramic elements of that section gained in a previous cycle when gas purified in the combustion chamber was drawn through that section to exhaust. After being preheated in that section, the incoming effluents enter the combustion chamber where their harmful components are oxidized. The purified effluent is then drawn out of the combustion chamber through others of the heat-exchange sections into the exhaust circuit for dispersion to the ambient atmosphere.
In such heat regenerative structures, the considerable lateral thrust of the ceramic heat exchange elements often required the use of steel tie rods extending horizontally between the front retaining wall ("hot face") and the rear retaining wall ("cold face"). These tie rods, as well, prevented bowing or deflection of the hot face due to heat. At the ends of these rods special washers and nuts were used to adjust the tension of the rods. Special horizontal pins were also lodged in the side edges of the front retaining wall for added structural strength. At incineration temperatures of up to about 1200.degree.-1600.degree. F., the hot face was often made of very expensive material such as high nickel-chromium content steel having low creep. For operation of the combustion chamber at even more elevated temperatures such as in the 1600.degree.-1800.degree. F. region, considerably more of this expensive steel would be required.
Moreover, the front retaining wall in conventional apparatus was often subjected to attack by the corrosive or other chemically destructive effects of some constituents of the effluents resulting in shortened life of such metallic walls. The front retaining walls of metal also had no substantial heat-exchange qualities.
Checker-board refractory walls have been used conventionally to provide heat-exchange properties, but, in general, they are so constructed as to be unable to withstand a considerable load. While U.S. Pat. No. 2,125,193 does show refractory blocks with grooves on one side which are disposed with the grooves of adjacent blocks to form an axial opening for permitting oxygen flor through the openings, there is no teaching of a horizontal arch-like wall consisting of a number of refractory blocks having axial passageways extending through them integrated into a circular combustion chamber wall. Such curved wall serves as an additional heat exchange assembly that can more economically withstand higher combustion temperatures and chemical attack and resist lateral thrust pressures.
It is therefore among the objects of the present invention to provide a refractory wall which:
(1) Is more temperature resistant than conventional walls used in heat-exchange apparatus. PA1 (2) Is less expensive to erect and to maintain than comparable known walls. PA1 (3) Is more resistant to chemical attack than conventional walls. PA1 (4) Is productive of greater heat-exchange effects than conventional metallic retaining walls. PA1 (5) Is capable of imparting greater strength to the overall furnace wall into which it is integrated than conventional metal-concrete constructions.